Direct and indirect MRI findings in ganglion cysts of the common peroneal nerve.

MRI findings in three cases of ganglion cyst of the common peroneal nerve are presented. In each case the cyst was imaged as an oval structure in transverse section section adjacent to the fibular neck. The cyst extended in a tubular fashion over several slices with an inferior extension towards the superior tibiofibular joint. Signal intensity was intermediate on T1- and high on T2-weighted images. In addition, increased signal on both T1- and T2-weighted images was noted throughout the peroneal compartment and was associated with clinical and EMG evidence of denervation. This has not been previously described but may be an important indirect sign which, when seen, should prompt a careful search in the region of the fibular neck for an underlying ganglion cyst of the common peroneal nerve.